This proposal outlines a program of research designed to investigate how visual information is used to guide locomotion to ensure safe and efficient navigation through the environment. More specifically, the long-term objective is to investigate the adaptive mechanisms that allow people to perform basic locomotor tasks in the face of variations in the dynamics of the body and the environment. Actors' movement capabilities are continually changing over both short and long time-scales as a result of injury, disease, neurological damage, aging, fatigue, growth, changes in load, and so on. Such variability has non-trivial consequences for the visual control of locomotion. The ability to adapt to these changes plays an essential role in supporting safe and efficient locomotion, and reducing the need for jerky, corrective movements that often result in losing balance, falling, and colliding with obstacles. An important next step in understanding the visual control of locomotion is to investigate how people perceive the world and control their movement in ways that take into account their ever-changing movement capabilities. The research described in this proposal is aimed at addressing the following questions about locomotor adaptation: (1) What components of optic flow drive adaptation to changes in locomotor capabilities? (2) To what extent does adaptation generalize to conditions and tasks that differ from those in which learning occurs? (3) To what extent should we attribute the reliability with which people take their movement capabilities into account to (a) internal adaptive mechanisms, and (b) information about one's locomotor capabilities that is picked up on the fly? Experiments will be conducted in a large-area virtual environment laboratory equipped with a head-mounted display and motion tracking equipment. Subjects will perform a variety of locomotor tasks, including turning toward goals, avoiding obstacles, intercepting moving targets, regulating gait to step on safe footholds, and selecting routes. The results will provide a foundation of knowledge for understanding the development, acquisition, and maintenance of locomotor skills, and for improving therapy programs that promote adaptation to changes that affect one's locomotor capabilities. PUBLIC HEALTH RELEVANCE: Locomotion is an integral part of many routine, daily activities. Changes in movement capabilities brought about by aging, injury, disease, fatigue, or use of a prosthetic limb pose a serious threat to one's ability to safely and efficiently navigate through complex, dynamic environments. The ability to adapt to these changes plays an essential role in supporting safe and efficient locomotion, and reducing the need for jerky, corrective movements that often result in losing balance, falling, and colliding with obstacles. The research described in this proposal is aimed at understanding the mechanisms that allow for adaptation of the visual-locomotor system. The results of this project will provide a basis for designing physical and occupational therapy programs that promote rapid and complete adaptation, allowing people whose movement capabilities become impaired to recover basic locomotor functions.